Composite material via in-situ polymerization of thermoplastic (meth)acrylic resins and its use

ABSTRACT

The present invention relates to a composite material obtained by in situ polymerization of a thermoplastic resin with a fibrous material. More particularly the present invention relates to a polymeric composite material obtained by in-situ polymerization of a thermoplastic (meth) acrylic resin and a fibrous material containing long fibers and its use, a process for making such a composite material and manufactured mechanical or structured part or article comprising this polymeric composite material.

This application claims benefit, under U.S.C. §119 or §365 of PCTApplication Number PCT/EP2012/004381, filed Oct. 19, 2012, and FrenchPatent Application Number FR 11.59553, filed Oct. 21, 2011.

FIELD OF THE INVENTION

The present invention relates to a composite material obtained by insitu polymerization of a thermoplastic resin with a fibrous material.

More particularly the present invention relates to a polymeric compositematerial obtained by in-situ polymerization of a thermoplastic(meth)acrylic resin and a fibrous material containing long fibers andits use, a process for making such a composite material and manufacturedmechanical or structured part or article comprising this polymericcomposite material.

Technical Problem

A composite material is a macroscopic combination of two ore more nonmiscible materials. The composite material constitutes at least of amatrix material that forms a continuous phase for the cohesion of thestructure and a reinforcing material with various architectures for themechanical properties.

The aim in using composite materials is to achieve a performance fromthe composite material that is not available from its separateconstituents if used alone. Consequently composite materials are widelyused in several industrial sectors as for example building, automotive,aerospace, transport, leisure, electronics, and sport notably due totheir better mechanical performance (higher tensile strength, highertensile modulus, higher fracture toughness) in comparison withhomogenous materials and their low density.

The most important class in view of volume in commercial industrialscale, are composites with organic matrices, where the matrix materialis a generally polymer. The principal matrix or continuous phase of apolymeric composite material is either a thermoplastic polymer or athermosetting polymer.

Thermosetting polymers consist of crosslinked three dimensionalstructures. The crosslinking is obtained by curing reactive groupsinside the so called prepolymer. Curing for example can be obtained byheating the polymer chains in order to crosslink and harden the materialpermanently. In order to prepare the polymeric composite material theprepolymer is mixed with the other component (for example glass beadsfor a particulate composite or short fibers for a fibrous composite) orthe other component is wetted or impregnated (for example woven nets)and cured afterwards. Example for prepolymers or matrix material forthermoset polymers are unsatured polyesters, vinylesters, epoxy orphenolic ones.

The disadvantage of a thermoset polymer matrix is its rigidity. Thematrix cannot be easily shaped in other forms. Once the polymer has beencured the form is fixed. This makes also difficult the recycling of thethermoset composite material, which are burned in a cement plant orthrown into a waste dump.

Thermoplastic polymers consist of linear or branched polymers, that arenot crosslinked. The thermoplastic polymers are heated in order to mixthe two constituents necessary for producing the composite material andto be cooled for setting. The limit in using thermoplastic polymers forthe fabrication of composite materials is their high viscosity in themolten state. The wetting or correct impregnation of the fibers by thethermoplastic polymer can only be achieved, if the thermoplastic resinis sufficiently fluid. In order to have a low viscosity or sufficientfluidity of the thermoplastic polymer the chain length (molecular mass)can be reduced. However a too low molecular weight has a negative impacton the performance of the composite material especially the mechanicalproperties. On the other hand the temperature of the thermoplasticpolymer could be increased in order to reduce the viscosity in animportant way. Consequently the continuous working temperature isrelatively high, above 200° C., influencing directly the economics(costs) of the composite material due to implication of high energycosts. Additionally thermoplastic polymers tend to degrade if thetemperature is very high, which is especially true for semicrystallinethermoplastic polymers that have high melting points as for examplepolyamides (for example PA6.6), polyethersulfon (PES), polyetherimide(PEI), polyetheretherketon (PEEK) or polyphenylene sulfide (PPS). Thisthermo induced degradation yields to a decreasing molecular weight ofthe polymer matrix important for the cohesion of the composite material.

Another way for impregnating the fibrous substrate is to dissolve thethermoplastic polymer in an organic solvent. However this methodrequires a lot of solvent that has to be evaporated. There areenvironmental issues in using large quantities of solvent in term ofenergy and pollution.

These are the limits or disadvantages for the preparation ofthermoplastic composite especially with continuous reinforcements. Thereis a need of a thermoplastic composite, that can be made by a process asa thermoset composite in terms of low initial viscosity in order toimpregnate the fibrous material and also having low production cycletimes, with a complex geometry and in series production.

The objective of the present invention is to solve the disadvantagesmentioned above.

The objective of the present invention is to have a polymeric compositematerial with satisfying mechanical properties that can be preparedeasily, be transformed and shaped into form, where the polymeric matrixhas a high molecular weight.

Another objective of the present invention is to have a polymericcomposite material with continuous fibers as reinforcements where pieceswith a large size can be produced fast and easily (short cycle times)and the polymeric matrix can be easily recycled and repaired.

Still another objective of the present invention is to have a process,where the fibrous material is correctly and completely wetted, wherepolymeric composite material with continuous fibers can be producedfast, for obtaining objects of large size and/or complex forms.

An additional objective of the present invention is to have a structuralpart comprising a thermoplastic composite material with satisfyingmechanical properties such as high stiffness and a modulus of at least15 GPa.

Still an additional objective of the present invention is to wetcompletely, correctly and in a homogenous way the fibrous substrateduring impregnation. Any defects of fiber wetting for example by bubblesand voids decrease the mechanical performance of the composite material.

Another objective of the present invention is the recycling of thecomposite material that do not meet quality standards or worn-outstructural parts. Under recycling is understood to recover at least apart of the used raw materials. This means grinding and reusing thethermoplastic polymer. This means also for example that the monomer fromthe thermoplastic matrix of the composite material can be recovered.

BACKGROUND OF THE INVENTION Prior Art

The document US2009/0169867 describes a composite material and methodsof making the same. The polymer matrix is obtained by curing or drying aaqueous binder composition comprising polymer particles of an emulsionpolymerization of ethylenically unsatured monomers including(meth)acrylic ester monomers. The substrate material of the compositemay be chosen from fibers.

The document U.S. Pat. No. 7,723,408 describes a composite material,wherein the matrix material is preferably a thermoplastic polymerincluding PMMA. Filler material includes metal coated glass fibers. Thematrix and the filler material are mixed, either by dry mixing or bysolution mixing.

The document EP0134973 describes fiber mat reinforced polyarylenesulfide composites and their method of preparation. The fibers arebrought into contact with the thermoplastic polymer either by heatingunder pressure the two components or the fiber mat is impregnated withslurry of poly phenylene sulfide in a carrier liquid followed by adrying step in order to remove the liquid followed as well by a heatingstep.

The document US 2002/0115748 describes a glass fiber reinforced styrenicthermoplastic composite containing an aminosilane coupling agent. Astyrene-copolymer is mixed with the coupling agent and glass fibers inorder to improve the surface adhesion between the matrix resin and theglass fibers. This method requires a third component which has to becompatible on one hand with the fibrous material and on the other handwith the polymer matrix.

The document CN1548168 describes a continuous carbon fiber reinforcedcomposite material for bone repair. The fibers are impregnated withmethyl methacrylate (MMA) or oligomers by pultrusion process or bodycasting. Flexible long chain acrylic monomers are added to the MMA at atleast 5 wt % in order to overcome the brittleness of the material.

The document FR1374046 describes a process for the polymerisation ofacrylic monomers; more particularly cured products from a (meth) acrylicmonomer-polymer syrup in presence of tin chloride and organic peroxides.

The prior art shows that PMMA is mentioned as thermoplastic polymermatrix for fibrous composites or that the acrylic monomers orfunctionalities are used for crosslinking thermoset matrices. Nothermoplastic fibrous composite material based on a methacrylic matrixaccording to the present invention is described.

No thermoplastic composite material is described where the fibrousmaterial and the thermoplastic (meth)acrylic matrix are brought intocontact before the final polymerization step according to the presentinvention.

BRIEF DESCRIPTION OF THE INVENTION

Surprisingly it has been discovered that a composite material comprising

-   -   (a) a polymeric thermoplastic (meth)acrylic matrix and    -   (b) a fibrous material as reinforcement        wherein the fibrous material has either at least an aspect ratio        of the fibre of at least 1000 or at least a two dimensional        macroscopic structure, has satisfying mechanical properties.

Surprisingly it has also been discovered that a composite materialcomprising

-   -   (a) a polymeric thermoplastic (meth)acrylic matrix and    -   (b) a fibrous material as reinforcement        wherein the fibrous material has either at least an aspect ratio        of the fibre of at least 1000 or at least a two dimensional        macroscopic structure can be easily prepared by a process        wherein the fibrous material and the polymeric thermoplastic        (meth)acrylic matrix were brought into contact by a wetting step        of the fibrous material with a liquid syrup comprising the        monomers for forming the polymeric thermoplastic (meth)acrylic        before the polymerization wherein the dynamic viscosity at        25° C. of the liquid syrup is between 10 mPa*s and 10000 mPa*s,        preferably between 50 mPa*s and 5000 mPa*s and advantageously        between 100 mPa*s and 1000 mPa*s.

It has also been found that a process for preparing a polymericcomposite material comprising

-   -   (a) a polymeric thermoplastic (meth)acrylic matrix and    -   (b) a fibrous material as reinforcement        that comprises a wetting step of the fibrous material with a        liquid syrup comprising the monomers for forming the polymeric        thermoplastic (meth)acrylic before the polymerization yield to        composites with the satisfying mechanical properties and the        other required characteristics for a composite material.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the present invention relates to a composite materialcomprising

-   -   (a) a polymeric thermoplastic (meth)acrylic matrix and    -   (b) a fibrous material as reinforcement        wherein the fibrous material has either at least an aspect ratio        of the fibre of at least 1000 or at least a two dimensional        macroscopic structure.

In a second aspect the present invention relates to a composite materialcomprising

-   -   (a) a polymeric thermoplastic (meth)acrylic matrix and    -   (b) a fibrous material as reinforcement        wherein polymeric thermoplastic (meth)acrylic matrix is chosen        from homopolymer or a copolymer of methyl methacrylate or        mixtures thereof.

In a third aspect the present invention relates to a process forpreparing a polymeric composite material comprising

-   -   (a) a polymeric thermoplastic (meth)acrylic matrix and    -   (b) a fibrous material as reinforcement        that comprises a wetting step of the fibrous material by a        liquid syrup comprising the monomers for forming the polymeric        thermoplastic (meth)acrylic before the polymerization.

In a fourth aspect the present invention relates to the use of acomposite material comprising

-   -   (a) a polymeric thermoplastic (meth)acrylic matrix and    -   (b) a fibrous material as reinforcement        wherein the fibrous material has either at least an aspect ratio        of the fibre of at least 1000 or at least a two dimensional        macroscopic structure in the field of automotive applications,        marine applications, railroad applications, sport, aeronautic        applications, photovoltaic applications and wind energy        applications.

In a fifth aspect the present invention relates to a manufacturedmechanical or structured part or article comprising such a polymericcomposite material.

By the term “(meth)acrylic” as used is denoted all kind of acrylic andmethacrylic monomers.

By the term “PMMA” as used are denoted homo- and copolymers ofmethylmethacrylate (MMA), for the copolymer of MMA the weight ratio ofMMA inside the PMMA is at least 70 wt %.

By the term “thermoplastic polymer” as used is denoted a polymer thatturns to a liquid or becomes more liquid or less viscous when heated andthat can take on new shapes by the application of heat and pressure.

By the term “thermosetting polymer” as used is denoted a prepolymer in asoft, solid or viscous state that changes irreversibly into aninfusible, insoluble polymer network by curing.

By the term “polymer composite” as used is denoted a multicomponentmaterial comprising multiple different phase domains in which at leastone type of phase domain is a continuous phase and in which at least onecomponent is a polymer.

By the term “impregnation” as used is denoted the penetration ofmonomeric, oligomeric or polymeric liquids or mixtures thereof into anassembly of fibers.

By the term “prepreg” as used are denoted sheets of a substrate thathave been impregnated with a curable prepolymer, or liquid reactants ora thermoplastic and are ready for the fabrication of laminates.

By the term “wetting” as used is denoted a process by which theinterface between a solid and a gas is replaced by an interface betweenthe same solid and a liquid.

By the term “high molecular weight” as used in the present invention isdenoted a weight average molecular weight Mw>50000 g/mol as measured byGPC.

By the term “aspect ratio” for a fiber as used in the present inventionis denoted the ratio between the length and the diameter of the fiber.

By the term “two dimensional structure” for a fibrous material as usedin the present invention is denoted that the fibers are not single, buttouch each other in order to form at least a two dimensional structurefor example in form of a nonwoven or a net or a fabric.

By the term “in-situ polymerization” as used in the present invention isdenoted that the final polymerization of the polymeric thermoplasticmatrix of the composite material takes place around the fibrousreinforcement material in order to obtain directly the thermoplasticcomposite material.

With regard to the thermoplastic (metha)acrylic matrix, one couldmention thermoplastic polymers as poly alkyl methacrylates or poly alkylacrylates. The alkyl group or the corresponding alkyl methacrylate oralkyl acrylate monomers consist of C1-C12 alkyl groups.

In a preferred embodiment the thermoplastic (meth)acrylic matrix is polymethyl methacrylate (PMMA).

The term “PMMA” denotes a methyl methacrylate (MMA) homopolymer or acopolymer comprising at least 70%, preferably at least 80%,advantageously at least 90% and more advantageously at least 95% byweight of methyl methacrylate or a mixture of at least one homopolymerand at least one copolymer of MMA, or a mixture of at least twohomopolymers or two copolymers of MMA with a different average molecularweight or a mixture of at least two copolymer of MMA with a differentmonomer composition.

The copolymer of methyl methacrylate (MMA) comprises from 70% to 99.7%by weight of methyl methacrylate and from 0.3 to 30% by weight of atleast one monomer having at least one ethylenic unsaturation that cancopolymerize with methyl methacrylate. These monomers are well known andmention may be made, in particular, of styrene, alpha-methylstyrene,acrylic and methacrylic acids and alkyl(meth)acrylates in which thealkyl group has from 1 to 12 carbon atoms. As examples, mention may bemade of methyl acrylate and ethyl, butyl or 2-ethylhexyl (meth)acrylate.Preferably the comonomer is an alkyl acrylate in which the alkyl grouphas from 1 to 4 carbon atoms.

In a preferred embodiment the copolymer of methyl methacrylate (MMA)comprises from 80% to 99.7% advantageously from 90% to 99.7% and moreadvantageously from 90% to 99.5% by weight of methyl methacrylate andfrom 0.3% to 20% advantageously from 0.3% to 10% and more advantageouslyfrom 0.5% to 10% by weight of at least one monomer having at least oneethylenic unsaturation that can copolymerize with methyl methacrylate.Preferably the comonomer is methyl acrylate or ethyl acrylate ormixtures thereof.

The weight average molecular weight of the thermoplastic (metha)acrylicmatrix should be high, meaning larger than 50 000 g/mol, preferablylarger than 100 000 g/mol.

The weight average molecular weight can be measured by size exclusionchromatography (SEC).

With regard to the reinforcement material, one can mention fibrousmaterial. The fibrous material can have different forms and dimensionseither one dimensional, two dimensional or three dimensional.

The one dimensional form is linear long fibers. The fibers may bediscontinuous or continuous. The fibers may be arranged randomly or as acontinuous filament parallel to each other. A fiber is defined by itsaspect ratio, which is the ratio between length and diameter of thefiber. The fibers used in the present invention are long fibers orcontinuous fibers. The fibers have an aspect ratio of at least 1000,preferably at least 1500, more preferably at least 2000, advantageouslyat least 3000 and most advantageously at least 5000.

The two dimensional form are fibrous mats or non woven reinforcements orwoven roving or bundles of fibers, which can also be braded.

The three dimensional form are for example stacked or folded fibrousmats or non woven reinforcements or bundles of fibers or mixturesthereof, an assembly of the two dimensional form in the third dimension.

The origins of the fibrous material can be a natural or a synthetic one.As natural material one can mention vegetable fibers, wood fibers,animal fibers or mineral fibers.

Natural fibers are for example sisal, jute, hemp, flax, cotton, coconutfibers, and banana fibers. Animal fibers are for example wool or hair.

As synthetic material one can mention polymeric fibers chosen fromfibers of thermosetting polymers, from thermoplastic polymers or theirmixtures.

The polymeric fibers can be made of polyamide (aliphatic or aromatic),polyester, polyvinylacohol, polyolefins, polyurethanes,polyvinylchloride, polyethylene, unsatured polysters, epoxy resins andvinylesters.

The mineral fibers can also be chosen from glass fibers especially oftype E, R or S2, carbon fibers, boron fibers or silica fibers. Thefibrous material of the present invention is chosen from vegetablefibers, wood fibers, animal fibers, mineral fibers, synthetic polymericfibers, glass fibers, carbon fibers or mixtures thereof.

With regard to the polymerization method for obtaining the thermoplastic(meth)acrylic matrix, one can mention radical, anionic polymerization orphotopolymerization.

The thermoplastic acrylic matrix is not cross linked. By not crosslinking is meant that no difunctional or more functional monomer withtwo or more polymerizable groups in the monomer is used. It is in thescope of the invention that secondary reactions might occur during thepolymerization, so that grafting or branching reactions might occur,including some cross linked points in some very few polymer chains. Inother words not cross linked is to be understood that no threedimensional network is obtained; that the polymer matrix is notswellable in a good solvent for the respective polymer, but the polymermatrix is still soluble in the solvent.

With regard to the radical initiator, they can be chosen from diacylperoxides, peroxy esters, dialkyl peroxides, peroxyacetals or azocompounds. The radical initiators which may be suitable are, forexample, isopropyl carbonate, benzoyl peroxide, lauroyl peroxide,caproyl peroxide, dicumyl peroxide, tert-butyl perbenzoate, tert-butylper(2-ethylhexanoate), cumyl hydroperoxide,1,1-di(tert-butylperoxy)-3,3,5-trimethyl-cyclohexane, tert-butylperoxyisobutyrate, tert-butyl peracetate, tert-butyl perpivalate, amylperpivalate, tert-butyl peroctoate, azobisisobutyronitrile (AIBN),azobisisobutyramide, 2,2′-azo-bis(2,4-dimethylvaleronitrile) or4,4′-azobis(4-cyanopentanoic). It would not be departing from the scopeof the invention to use a mixture of radical initiators chosen from theabove list. The preferred radical initiator is azobisisobutyronitrile.

The content of radical initiator with respect to the monomers of themixture which is cast in the mould varies from 100 to 2000 ppm (byweight), preferably between 200 and 1000 ppm, by weight.

Another ingredient can also be a chain-limiting agent in order tocontrol the molecular weight, for example γ-terpinene or terpinolene, atcontents of between 0 and 500 ppm and preferably between 0 and 100 ppm,with respect to the monomers of the mixture.

No metal comprising additives as activators for catalytically acceleratethe polymerization reaction are added. These concerns especially tinbased compounds as tin chloride.

The polymeric composite according to the invention comprises a fibrousmaterial and the polymeric thermoplastic (meth)acrylic matrix. The twoare brought into contact by a wetting step of the fibrous material witha liquid syrup comprising the monomers for forming the polymericthermoplastic (meth)acrylic before the polymerization.

A simple monomer or a monomer mixture is too liquid for the respectivemethods of preparation of the polymeric composite material of thepresent invention, especially for the correct and complete wetting andimpregnation of the fibrous material. Therefore the viscosity has to beadapted by increasing it.

In one embodiment the viscosity is increased by a prepolymerisation ofthe monomer. Oligomers are obtained by the prepolymerization.

In another embodiment the viscosity is increased by using monomers ormonomer mixtures with dissolved oligomers or polymers. This solution iscommonly referred to as “syrup” or “prepolymer”. The oligomer or polymeris soluble in the monomer. This oligomer or polymer could be a PMMA or astyrene maleic anhydride copolymer (SMA). Preferably the oligomer orpolymer is a methyl methacrylate (MMA) homopolymer or copolymercomprising at least 70%, preferably at least 80%, advantageously atleast 90% and more advantageously at least 95% by weight of methylmethacrylate.

The monomer or the monomers in the syrup that will form afterpolymerization a part of thermoplastic (metha)acrylic matrix present atleast 40% by weight, preferably 50% by weight, advantageously 55% byweight and more advantageously 60% by weight of total liquid syrup.

The monomer or the monomers in the syrup that will form afterpolymerization a part of thermoplastic (metha)acrylic matrix present atmost 99% by weight, preferably at most 95% by weight, advantageously atmost 90% by weight and more advantageously at most 85% by weight, evenmore advantageously at most 82% and most advantageously at most 80% byweight of total liquid syrup.

The oligomers or polymers in the syrup that will form also afterpolymerization a part of thermoplastic (metha)acrylic matrix present atleast 1% by weight, preferable at least 5% by weight, advantageously atleast 10% by weight, more advantageously at least 15% by weight and evenmore advantageously at least 18% and most advantageously at least 20% byweight of total syrup.

The oligomers or polymers in the syrup that will form also afterpolymerization a part of thermoplastic (metha)acrylic matrix present atmost 60% by weight, preferable at most 50%, advantageously at most 40%and more advantageously at most 35% by weight of total syrup.

The monomer or the monomers in the syrup that will form afterpolymerization a part of thermoplastic (metha)acrylic matrix presentfrom 40% to 95% by weight, preferably from 50% to 90% by weight,advantageously from 55% to 85% by weight and more advantageously from60% to 80% by weight of total liquid syrup. Accordingly the oligomers orpolymers in the syrup that will form also after polymerization a part ofthermoplastic (metha)acrylic matrix present from 60% to 5% by weight,preferably from 50% to 10% by weight, advantageously from 15% to 45% byweight and more advantageously from 20% to 40% by weight of total liquidsyrup.

The dynamic viscosity of the prepolymer or liquid syrup is between 10mPa*s and 10000 mPa*s, preferably between 50 mPa*s and 5000 mPa*s andadvantageously between 100 mPa*s and 1000 mPa*s. The viscosity of thesyrup can be easily measured with a Rheometer. The dynamic viscosity ismeasured at 25° C. The liquid syrup has a Newtonian behaviour, meaningno shear thinning, so that the dynamic viscosity is independent of theshearing in a rheometer or the speed of the mobile in a viscometer.

If the viscosity of the liquid prepolymer or syrup at a giventemperature is too high for the correct impregnation, it is possible toheat the syrup in order to have a more liquid syrup within the beforementioned dynamic viscosity interval at the respective temperatureduring which the impregnation takes place for the sufficient wetting andcorrect and complete impregnation of the fibrous material.

The liquid syrup according to the present invention does not contain anyadditional solvent voluntary added.

With regard to the structure or composition of the polymeric compositematerial of the present invention, it comprises at least 20% by weightof fibrous material, preferable at least 40% by weight of fibrousmaterial advantageously at least 50% by weight of fibrous material andadvantageously at least 55% by weight of fibrous material based on thetotal composition.

The polymeric composite material of the present invention, it comprisesat most 99% by weight of fibrous material, preferable at most 95% byweight of fibrous material advantageously at most 90% by weight offibrous material and advantageously at most 80% by weight of fibrousmaterial based on the total composition.

The structure of the composite concerns also laminates. Several layersor sheets of the thermoplastic fibrous composite material may be bondedtogether by lamination.

The polymeric composite may comprise also other additives and fillers.All the additives and fillers can be added to the liquid syrup beforewetting and polymerization.

As additives one can mention organic additives as impact modifiers orblock copolymers, thermal stabilizers, UV stabilizers, lubricants andmixtures thereof.

The impact modifier is in the form of fine particles having an elastomercore and at least one thermoplastic shell, the size of the particlesbeing in general less than 1 μm and advantageously between 50 and 300nm. The impact modifier is prepared by emulsion polymerization. Theimpact modifier content in the polymeric thermoplastic matrix is between0 and 50%, preferably between 0 and 25%, and advantageously between 0and 20% by weight.

As fillers one can mention carbon nanotubes or mineral charges includingmineral nano charges (TiO2, silica).

No metals in the thermoplastic composite material such as tin arepresent coming from accelerators added for the polymerization step.

The composite does not contain any additional solvent voluntary added,since the syrup did not contain any additional solvent for theimpregnation step.

With regard to the method of preparation of the polymeric compositematerial, several methods could be used in order to prepare threedimensional samples. One can mention lamination, pultrusion, infusion,vacuum bag moulding, pressure bag molding, autoclave molding, resintransfer moulding (RTM), reinforced reaction injection molding (R-RIM)and variants thereof, press molding, filament winding, compressionmolding or wet lay up.

All methods comprise the steps of wetting the fibrous material with theliquid syrup comprising the monomers for forming the polymericthermoplastic (meth)acrylic matrix before the polymerization step.

The final molecular weight of the thermoplastic polymeric matrix isobtained during one of the mentioned methods for the preparation of thepolymeric composite material.

In the pultrusion method a long continuous product of constant crosssection is produced. The fibers coming from creels are wetted andimpregnated with the liquid resin in a resin bath followed bypreforming, shaping and polymerization.

Resin transfer molding is a method using a two sided mold set whichforms both surfaces of composite material. The lower side is a rigidmould. The upper side can be a rigid or flexible mould. Flexible mouldscan be made from composite materials, silicone or extruded polymer filmssuch as nylon. The two sides fit together to produce a mould cavity. Thedistinguishing feature of resin transfer moulding is that thereinforcement materials are placed into this cavity and the mould set isclosed prior to the introduction of matrix material. Resin transfermoulding includes numerous varieties which differ in the mechanics ofhow the resin is introduced to the reinforcement in the mould cavity.These variations include everything from vacuum infusion to vacuumassisted resin transfer moulding (VARTM). This process can be performedat either ambient or elevated temperature. Ambient temperature meansbetween 10° C. and 50° C. Elevated temperature means up to 200° C.Preferably elevated temperature is from 50° C. up to 160° C.

With the infusion method the liquid prepolymer syrup does have to have aviscosity adapted towards the preparation method of the polymericcomposite material. The syrup is aspired into the fibrous materialpresent in a special mold by application of a slight vacuum. The fibrousmaterial is infused and completely wetted by the liquid prepolymersyrop.

One advantage of this method is the high amount of fibrous material inthe composite.

The preferred methods for preparing the composite materials are methodswere the liquid resin of the not yet polymerized matrix material istransferred to the fibrous material more preferably in a mold.

Advantageously the wetting step of the fibrous material is made in aclosed mold, by resin transfer molding or by infusion.

More advantageously the wetting step of the fibrous material and thepreparation of the thermoplastic composite material take place in thesame mold, which is a closed mold. The mold is opaque towards visibleand ultraviolet radiation at least on one side.

A closed mold will amongst other things avoid and reduce the evaporationof the monomer and protect the environment.

Still another aspect of the present invention is a manufacturing processfor manufacturing mechanical or structured parts or articles comprisingthe thermoplastic composite material according to the inventioncomprising following steps:

-   -   a) impregnating a fibrous substrate with a liquid syrup,    -   b) polymerising the liquid syrup impregnating said fibrous        substrate.

Preferably the impregnation of the fibrous substrate in step a) is madein a closed mold.

Advantageously the step a) and step b) are made in the same closedmould.

The mold is opaque towards visible and ultraviolet radiation at least onone side of the mold.

Using the same closed mold will avoid the transfer of the material afterimpregnation and polymerizing in a closed mold will guarantee a gooddistribution of the heat, having a satisfying yield of polymerizationand eventually evaporation of the monomer(s).

With regard to the use of polymeric composite material, one can mentionautomotive applications, nautical applications, railroad applications,sport, aeronautic and aerospace applications, photovoltaic applicationsand wind energy applications.

The polymeric composite material according to the invention is used tomanufacture mechanical or structured parts or articles particularlythree-dimensional mechanical or structured parts.

Due to the complete, correct and in a homogenous wetting of the fibroussubstrate during impregnation there are no defects of fiber wetting forexample by bubbles and voids decrease the mechanical performance of thecomposite material.

The manufactured mechanical or structured parts or articles comprisingpolymeric composite material according to the invention do not compriseessentially any pores. By pore is meant a spherical void with a diameterof at least fpm or larger or an elongated ellipsoidal void in form of anoblate with a smallest principal axe of at least 0.5 μm or larger. By“comprising essentially no pores” is meant that the pores represent lessthen 1 vol %, preferably less then 0.5 vol % and more preferably lessthen 0.2 vol % of the total volume of the thermoplastic compositematerial

With regard to the use of manufactured mechanical or structured parts orarticles, one can mention automotive applications, nauticalapplications, railroad applications, sport, aeronautic and aerospaceapplications, photovoltaic applications, computer related applications,telecommunication applications and wind energy applications.

Particularly the three-dimensional mechanical or structured part is aautomobile part, boat part, train part, sport article, plane orhelicopter part, space ship or rocket part, photovoltaic module part,wind turbine part, furniture part, construction or building part,telephone or cell phone part, computer or television part, printer andphotocopy part.

With regard to the recycling of the thermoplastic composite material ormanufactured mechanical or structured part or article comprising thethermoplastic composite material it can be made by grinding ordepolymerization of the thermoplastic polymer. Grinding is mademechanically in order to obtain smaller parts of pieces. As thestructured part compromises thermoplastic polymer, this polymer can beheated, and the pieces again transformed in a certain limit in order toobtain a recycled object.

Preferably the structured part comprising the thermoplastic composite isheated for making a pyrolysis or thermal decomposition of the PMMA andrecovering the methyl methacrylate (MMA) as monomer.

Advantageously at least 50 wt % of the MMA present in the polymer arerecovered by thermal decomposition.

The structured part is heated at a temperature of at least 200° C. andno more than 400° C.

[Methods]

The weight fraction of the fibres in the composite material is obtainedby the norm NF EN 2564 (“Serie aerospatiale—Stratifies de fibres decarbone Determination de la teneur en fibres en resine et du taux deporosite”)

The mechanical properties in traction are characterized by following thenorm ISO 527-4 (“Plastics—Determination of tensile properties—Part 4:Test conditions for isotropic and orthotropic fibre-reinforced plasticcomposites”) type 3.

The mechanical properties in compression are characterized by followingthe norm ISO 14126:1999 (“Fibre-reinforced plasticcomposites—Determination of compressive properties in the in-planedirection”) type A1 following a set up of Celanese type.

The mechanical properties in of 3 points bending are characterized byfollowing the norm NF EN 2562 (“Carbon fibre reinforced plastics.Unidirectional laminates. Flexural test parallel to the fibredirection”) type 1.

EXAMPLES

FIG. 1 gives a simple scheme of infusion method and the mold (1). Thelower part (2) of the mold (1) is made of a rigid and opaque material(2), while the upper part (3) of the mold (1) is made of a flexiblematerial (3) that hermetically closes the mold with help of joints (4)that tightly seal the mold. Between the lower (2) and the upper (3) partof the mold (1) the fibrous material (5) is placed. The liquid resin isdistributed with a distribution line (6) that goes inside the mold and avacuum line (7). By applying a slight vacuum the liquid resin infusesthe fibrous material (5) placed between the two parts of the mold (1).

Composite materials are prepared by infusion process. This processconsist of drawing in the prepolymer or syrup (liquid resin) through astack of fabrics (fibrous material) which are placed between a rigidclosed mold (rigid opaque glass or metal plate, lower part of the mold)and a flexible plastic film at the outer perimeter or upper part of themold. For doing this a vacuum is applied between 0.6 bar and 0.95 bar.

The infusion process requires the vacuum only for transferring the syrupthrough the fabrics.

Example 1 (Invention)

8 folded glass fabrics (glass E plain weave HexForce® 01717 820 TF970from the company Hexcel with a nominal weight of 160 g/m²) with adimension of 30 cm×20 cm has been folded at a glass sheet which servesas mould for obtaining a thickness of 2 mm of the composite piece.

A syrup is prepared by dissolving 25 wt % of polymethyl methacrylate(PMMA V825 from Altuglas) in methyl methacrylate (MMA) in presence of325 ppm AIBN (azo bis isobutyronitrile) and 35 ppm terpinolene (1,4paramenthadiene). The dissolving takes place at ambient temperature at25° C. during 48 hours. The viscosity of the syrup solution is 513mPa*s, measured at ambient temperature (25° C.) with a cone/platerheometer from the Brookfield company.

The formed prepolymer syrup is infused with the help of a vacuum pump,which allows transferring the syrup through the fabric. The infusion ofthe sheet happens during 3 minutes, the speed of the infusion front is100 mm/min. The infused sheet is placed in an oven for 4 hours at 60° C.and an addition heating step of 30 minutes at 125° C. for completepolymerization of the PMMA (reaching a conversion of nearly 100% of themonomer).

The polymeric composite is recovered by separation of the differentfilms of the infusion after the complete polymerization and demoulding.

Example 2 (Invention)

The glass fabric from example 1 is replaced by a fabric of carbon fibres(HexForce® 46285 U 1200 from the company Hexcel).

Example 3 (Comparative Example)

Example 1 is repeated with syrup containing only methyl methacrylate(the 25 wt % PMMA are replace by MMA), AIDN and terpinolene. Theviscosity of the syrup is <5 mPa*s. During the impregnation by infusion,the speed of the infusion front is too fast (>500 mm/min) and the syrupcould not completely wet and impregnate the glass fabric. After curingin an oven (4 hours at 60° C. followed by 30 minutes at 125° C.),following demolding, the composite is incomplete and has no goodmechanical performances. Dry non wetted glass fibers are present in themiddle of the composite.

Example 4 (Comparative Example)

8 folded glass fabrics (glass E plain weave HexForce® 01717 820 TF970form the company Hexcel with a nominal weight of 160 g/m2) with adimension of 30 cm×20 cm has been folded at a glass sheet which servesas mould for obtaining a thickness of 2 mm of the composite piece.

The fabric is infused with a vinylester resin DION® IMPACT 9102-75 fromthe company Reichold in which 1.5 wt % NOROX® CHM-50 a peroxide from thecompany Noerac has been added, in order to initiate the crosslinking ofthe resin. The viscosity of the resin is 200 mPa*s. The crossslinkingreaction of the resin takes place during 24 hours at ambienttemperature, followed by a post curing during 2 hours at 65.5° C. andadditional 2 hours at 121° C. in an oven.

The polymeric composite is recovered by separation of the differentfilms of the infusion after the complete polymerization and demoulding.

Example 5 (Comparative Example)

The glass fabric from example 4 is replaced by a fabric of carbon fibres(HexForce® 46285 U 1200 from the company Hexcel).

The sheets obtained by examples 1, 2, 4 and 5 are characterized bymechanical properties in traction, compression and flexion. The sheetobtained in example 3 could not be characterized.

TABLE 1 mechanical properties Exam- ple 1 Example 2 Example 4 Example 5Class of thermo- thermo- thermoset thermoset composite plastic plasticWeight ratio 61.4 60.8 69.0 63.4 of fibres [%] Traction Modulus of 16.055.1 20.6 48.0 cord (0.05-0.25% of deformation [GPa] Tensile 325 723 410647 stress at break [MPa] Deformation 2.38 1.34 2.53 1.33 at break [%]Compression Compressive 112 154 184 239 stress at break [MPa] FlexionFlexural 178 347 239 523 stress at break [MPa]

The comparative examples 4 and 5 with a thermoset crosslinked polyestershow, that with the thermoplastic composite according to the presentinvention it is possible to obtain comparable mechanical properties.

Due to the thermoplastic matrix of examples 1 and 2 the form of thecomposite can be changed and adapted, for example by welding.

The invention claimed is:
 1. A thermoplastic polymeric compositematerial comprising (a) a polymeric thermoplastic (meth)acrylic matrix,consisting of at least one acrylic copolymer comprising at least 70% byweight of methyl methacrylate monomer units and from 0.3 to 30% byweight of at least one monomer having at least one ethylenicunsaturation that can copolymerize with methyl methacrylate; and (b) atleast 40 weight percent of a fibrous material, based on the total weightof the polymeric composite material as reinforcement, wherein thefibrous material comprises either a fiber with an aspect ratio of thefiber of at least 1000, or the fibrous material has a two dimensionalmacroscopic structure, and wherein said fibrous material and thepolymeric thermoplastic (meth)acrylic matrix were brought into contactby a wetting step of the fibrous material with a liquid syrup comprisingthe monomers for forming the polymeric thermoplastic (meth)acrylicmatrix before polymerization, and wherein the dynamic viscosity at 25°C. of the liquid syrup is between 10 mPa*s and 10000 mPa*s in a closedopaque mold.
 2. The polymeric composite according to claim 1, whereinthe polymeric thermoplastic (meth)acrylic matrix is selected from thegroup consisting of a mixture of at least one homopolymer and at leastone copolymer of MMA, a mixture of at least two homopolymers or twocopolymers of MMA having different weight average molecular weights, andmixture of at least two copolymers of MMA with different monomercomposition.
 3. The polymeric composite according to claim 1, whereinthe copolymer of methyl methacrylate (MMA) comprises from 80% to 99.7%by weight of methyl methacrylate and from 0.3% to 20% by weight of atleast one monomer having at least one ethylenic unsaturation that cancopolymerize with methyl methacrylate.
 4. The polymeric compositeaccording to claim 1, wherein the fibrous material is selected from thegroup consisting of vegetable fibers, wood fibers, animal fibers,mineral fibers, synthetic polymeric fibers, glass fibers, carbon fibersand mixtures thereof.
 5. The polymeric composite according to claim 1,wherein the fibrous material is in the form of fibrous mats, a nonwoven,woven roving or bundles of fibers, which can also be braided, ormixtures thereof.
 6. A process for preparing the polymeric compositematerial according to claim 2, comprising the steps of a) wetting orimpregnating a fibrous material with a liquid syrup comprising at least40% of a monomer or monomers for forming the polymeric thermoplastic(meth)acrylic; and b) polymerizing said liquid syrup that is wetting orimpregnating said fibrous material, wherein the wetting step of thefibrous material is made in a closed mold.
 7. The process for preparingthe polymeric composite material according to claim 6, wherein thedynamic viscosity at 25° C. of the liquid syrup is between 10 mPa*s and10000 mPa*s.
 8. The process for preparing the polymeric compositematerial according to claim 6, wherein the liquid syrup comprisesoligomers or polymers dissolved in said monomer or the monomers.
 9. Theprocess for preparing the polymeric composite material according toclaim 6, wherein the wetting or impregnating step of the fibrousmaterial is made in a closed mold, by resin transfer molding or byinfusion.
 10. The process for preparing the polymeric composite materialaccording to claim 6, wherein the monomers for forming the polymericthermoplastic (meth)acrylate are chosen so that the polymericthermoplastic (meth)acrylate is a copolymer of methyl methacrylate (MMA)comprising from 80% to 99.7% by weight of methyl methacrylate and from0.3% to 20% by weight of at least one monomer having at least oneethylenic unsaturation that can copolymerize with methyl methacrylate.11. The process for preparing the polymeric composite material accordingto claim 8, wherein the dissolved oligomers or polymers are chosen fromPMMA or a styrene maleic anhydride copolymer.
 12. The process forpreparing the polymeric composite material according to claim 8, whereinthe dissolved oligomers or polymers is a methyl methacrylate (MMA)homopolymer or copolymer comprising at least 70%, by weight of methylmethacrylate.
 13. The process for preparing the polymeric compositematerial according to claim 6, wherein the monomer or the monomers ofthe liquid syrup are present at 50% or greater by weight.
 14. Themanufacturing process according to claim 13 wherein the impregnation ofthe fibrous substrate in step a) is made in a closed mold and the stepa) and step b) are made in the same closed mold.
 15. The polymericcomposite material of claim 1, wherein said composite material is amanufactured mechanical or structured part or article.
 16. The polymericcomposite material of claim 15, wherein said manufactured mechanical orstructured part or article consists essentially of no pores.
 17. Thepolymeric composite material of claim 15, wherein said manufacturedmechanical or structured part or article is a part or article for use inautomotive applications, marine applications, railroad applications,sport, aeronautic and aerospace applications, photovoltaic applicationsor wind energy applications.
 18. The polymeric composite material ofclaim 15, wherein said manufactured mechanical or structured part orarticle is a part selected from a automobile part, boat part, trainpart, sport article, plane or helicopter part, space ship or rocketpart, photovoltaic module part, wind turbine part, furniture part,construction or building part, telephone or cell phone part, computer ortelevision part, and printer or photocopy part.
 19. The polymericcomposite material of claim 1, wherein said liquid syrup does notcontain any additional voluntary added solvent.
 20. The polymericcomposite material of claim 1, wherein said liquid syrup does notcontain any metal additives as activators for catalytically acceleratingthe polymerization reaction.
 21. The polymeric composite material ofclaim 20, wherein said metal additives not in said liquid syrup aretin-based compounds.